1. Field of Invention
The present invention relates to power fold mechanisms for external rear vision mirrors of motor vehicles.
2. Background of the Invention
Motor vehicles typically have two external rear vision mirror assemblies. The mirror assemblies typically have a mirror head that is designed to rotate about a substantially vertical pivot axis in both forward and rearward directions. The mirror head is typically held in its driving position by a detent which allows manual movement of the mirror head to a parked position and manual movement to a forward position. There are a number of reasons for this. One reason is safety. By having a mirror that can “break away” to move from a deployed position to a parked or forward position, injury to people can be minimised. Furthermore, damage to the mirror head can be minimised by allowing it to move when it hits obstructions. It is also useful to have a mirror head that can be parked, that is rotated to a position substantially parallel to the side of the vehicle, so as to narrow the effective width of the vehicle. This is particularly useful when the vehicle is parked in or is travelling along narrow or congested roadways. It is also useful for loading vehicles onto trucks for transport to be able to park the mirror heads.
Modern external rear vision mirrors, in addition to having a detent mechanism to hold the mirror head in a deployed position while at the same time enabling forward folding and rearward folding of the mirror head, also have electric drive systems to allow the operator to drive the head at least to its parked position. Some external rear view mirror assemblies have more sophisticated electric systems that allow the operator to redeploy the mirror head to a drive position after it has been manually pushed forward or rearward. These mirror systems are typically referred to as power fold mirrors.
Power fold mirrors typically employ power fold mechanisms that hold the mirror head against rotation in one direction with respect to the mirror base. This is usually achieved using a non-back-drivable gear train (such as a gear train employing a worm gear). As a result, the gear train is subject to significant forces and or torques resulting from wind, road and static forces. Thus, the power fold mechanism must be strong, rigid and have a good fastening system to both the mirror base and to the mirror frame. These requirements increase complexity and cost. They also mean that the mirror assembly must be specifically designed as a power fold mirror assembly with many different components to a non-power fold system.
An external rear view mirror for automobiles is disclosed in U.S. Pat. No. 6,022,113 (Stolpe et al). The rear view mirror disclosed by that US patent has a non-back-drivable worm gear that locks a gear wheel in place. The gear wheel can be driven by the worm gear but cannot drive back through the worm gear. Thus, the gear wheel can be used (and is used) as a stop, holding the drive housing 4 and hence the mirror head against fold path limiter stop cams on the mirror base 2. As a result, the gear train is subject to significant forces resulting from wind, road and static forces while it is held in the drive position. These forces are transmitted from the mirror head 3 to the powerfold housing 4 via a case frame in the mirror head. The force is then further transferred through the worm and gear teeth to the detent system on the bottom of the gear. Here it meets the reaction force provided by the spring that clamps the system. If the force supplied is great enough, the detent system will disengage compressing the spring and allowing the mirror head to manually rotate it to the parked position.
As should be apparent from the above, with the mirror described in U.S. Pat. No. 6,022,113, the powerfold housing 4, the drive train including gear wheel 6 and worm gear 11 are subject to significant forces and must be strong and rigid. Furthermore, the mirror of U.S. Pat. No. 6,022,113 cannot really be modified to become a non-powerfold mirror assembly.
It is an object of the present invention to provide an improved power fold mechanism that overcomes at least some of the problems outlined above or at least offers a useful choice.